By adding different electron donor moieties to the ancillary ligand in ruthenium(ii) phenanthroimidazole complexes, we successfully designed near infrared light emitting complexes suitable for light emitting electrochemical cells (LECs).

Turn-on time is a key factor for lighting devices to be of practical application. To decrease the turn-on time value of a deep-red light-emitting electrochemical cells (DR-LECs), two novel approaches based on molecularly engineered ruthenium phenanthroimidazole complexes were introduced. First, we found that with the incorporation of ionic methylpyridinium group to phenanthroimidazole ligand, the turn-on time of the DR-LECs device was dramatically reduced, from 79 to 27 s. By complexation of ruthenium emitter with Ag+, the turn-on time was improved by 85%, and the EQE of DR-device was increased from 0.62 to 0.71%. These results open a new avenue in decreasing the turn-on time without adding ionic electrolytes, leading to an efficient LEC.

No abstract

Light-Emitting Electrochemical Cells (LECs) with a simple device structure ITO/Ru complex/Ga:In were prepared by using heteroleptic ruthenium(ii) complexes containing 2-(2-hydroxyphenyl)-1-(4-bromophenyl)-1h-imidazo[4,5-f][1,10]phenanthroline (hpbpip) as the π-extended ligand. After ancillary ligand modification, the [Ru(hpbpip)(dmbpy)2](ClO4)2 complex shows a deep red electroluminescence emission (2250 cd m(-2) at 6 V) centered at 685 nm, 65 nm red-shifted compared to the [Ru(bpy)3](ClO4)2 benchmark red-emitter at a very low turn voltage (2.6 V), demonstrating its potential for low-cost deep-red light sources. Moreover, the PL quantum yield of the [Ru(hpbpip)(bpy)2](ClO4)2 complex was revealed to be higher (0.121) than the benchmark standard [Ru(bpy)3](2+) (0.095).

Near-infrared light-emitting electrochemical cell (NIR-LEEC) has emerged as a new and promising lighting sourcewhich could serve as low-cost alternatives in NIR light-emitting sources which are typically expensive. LECs were also shown advantages such as light weight, simplicity and low operation voltages. However, only a few examples of NIR-LEEC are reported in which external quantum efficiency(EQE) of devices limited to 0.1%. Here, we report, efficient NIR-LEEC based of two novel binuclear ruthenium phenanthroimidzole complex which differ by employing the type of ancillary ligand including 2, 2′bipyridine (bpy) (B1) and 4, 4′ dimethyl bpy (B2) that realize maximum EQE of 0.14 and 0.68% and extremely long excited state lifetimes of 220 and 374 ns for thin film were estimated, respectively, indicating that influences of substitution on ancillary ligand. Moreover, this substitution dramatically influences other electroluminescence metrics including decreasing turn on voltage from 4.5 to 3.1 V, increasing maximum luminance (Lmax) from 193to 742 cd.m−2 and increasing lifetime from 539 to 1104 second, which are the best value among the binuclear ruthenium polypyridyl complexes to date.

Electroplex emission is rarely seen in ruthenium polypyridyl complexes, and there have been no reports from light-emitting electrochemical cells (LECs) to date. Here, near-infrared (NIR) emission via the electroplex mechanism in a LEC was reported.

We report on an organic electroluminescent device with simplified geometry and emission in the red to near infrared (NIR) spectral region which, has the lowest turn-on voltage value, 2.3 V, among light emitting electrochemical cells (LEECs). We have synthesized and characterized three novel ruthenium π-extended phenanthroimidazoles which differ on their N^N ligands. The use of dimethyl electron donating groups along with the π-extended phenanthroimidazole moiety promotes ambipolar transport thereby avoiding the use of additional charge transport layers. Furthermore, a facile cathode deposition method based on transfer of a molten alloy (Ga:In) on top of the active layer is deployed, thus avoiding high vacuum thermal deposition which adds versatile assets to our approach. We combine ambipolar charge transport organic complex design and a simple ambient cathode deposition to achieve a potentially cost effective red to NIR emitting device with outstanding performance, opening new avenues towards the development of simplified light emitting sources through device optimization.

In this work, we have introduced a star‐shaped sensitizer for dye sensitized solar cells (DSSCs) consist of three anchoring groups of benzene sulfonic acid with a significant improvement of interfacial electron transfer rate of dye/TiO2‐anatase nanostructures compared to corresponding sensitizers containing only one anchoring group. Physical chemistry aspect of the robust star‐shaped sensitizer has been investigated, employing the Current over Voltage analysis (I−V) and Transient Absorption Spectroscopy (TAS) methods. The computational studies based on density functional theory (DFT) and quantum calculations were clearly indicated that the rate of the Interfacial electron transfer (IET) significantly depends on the binding mode of a sensitizer to semiconductor surface and the nature of the electronic population in lowest unoccupied molecular orbitals (LUMOs) that initially localized on the adsorbate molecule, which is in a good agreement with experimental results. Our main result is that, among different possible binding modes of anchoring group to TiO2 surface, the bridging mode has the shortest life time of 28 fs in the presence of visible light as the excitation source. To investigate negative effect of the sensitizer molecules aggregation on TiO2 surface, on the performance of the cell, was examined the dye loading time on TiO2 surface for 10, 16 and 20 hours, which 16 hours of dye loading on surface exhibited the best DSSC performance. Moreover, transient absorption studies consistently show that the star‐shaped dye (consist of three anchoring groups) has better performance compared to the other dyes (consist of one anchoring groups) (1 and 3), in all aspects of critical parameters for DSSCs, including electron lifetime in TiO2, electron injection, dye regeneration and recombination resistance. The present work explains the fundamental physical chemistry aspects of the excited‐state in star‐shaped ruthenium polypyridyl complexes, along with opening new insight into the design of new sensitizers for enhancing the interfacial electron transfer rate and lowering the charge recombination process, which results in high power conversion efficiency of DSSC.